Fourth Degree of Organic Structure

Nerves terminating in a longitudinal ganglionic chord or in a brain without a spinal chord; respiration with gills; arteries and veins for circulation.

[The Crustaceans, the Annelids, the Cirripeds and the Mollusks]

CRUSTACEANS

(Seventh Class of the Animal Kingdom)

Oviparous animals, having articulated bodies and limbs, a crustaceous skin, several pairs of jaws, eyes and antennae in the head; respiration by gills; a heart and vessels for circulation.

Observations

Some significant changes in the organic structure of the animals of this class indicate that in forming the crustaceans nature has succeeded in making considerable progress in the organic structure of animals.

First, the method of respiration is here entirely different from that used in the arachnids and insects. And this method, made up of organs called gills, is going to continue right up to the fish. Trachaea do not appear again, and the gills themselves will disappear when nature is able to create a cellular lung.

Then, the circulation (which in the arachnids consists of only a simple outline) is fully established in the crustaceans, where we see a heart and arteries for sending out blood to the different parts of the body and veins which bring this fluid back to the principal organ responsible for its motion.

We find again in the crustaceans the style of articulations which nature has universally used in the insects and the arachnids, to facilitate muscular movement with the help of indurations of the skin, but from this point on nature will abandon this method of setting up an organic structure which no longer will require it.

The majority of crustaceans live in water, either fresh or brackish or salt. Some nonetheless remain on the earth and breathe air with their gills. All of them feed only on animal material.

Table of Crustaceans

First Order: Sessile-Eyed Crustaceans

Sessile and immobile eyes

Wood-louse Ligia Asellus Cyamus Shrimp Caprella

Cyclops Zoea

Cephaloculus Amymone Daphnia Lunceus Osole Limulus Coligus Polyphemus

Second Order: Stalk Eyed Crustaceans

Two distinct eyes raised on mobile stalks

(1) Elongated tail, equipped with swimming blades or hooks or hairs

Branchiopod Squilla Palaemon Galathea Ecrevissa Pagurus (hermit crab)

Ranina

Crangon Palinurus (rock lobster) Scyllarus Albunea Hippia Corystes Porcellana

(2) Short tail, bare, and held against the under part of the abdomen

Pinotheres Leocosia Arctopsis Maia

Orithyia Podophtalmus Portunus

Dorippe Plagusia Grapsus Ocypode Calappa Hepatus Dromia Cancer